The present invention is generally in the area of methods and devices to obtain vascular tissue grafts and more specifically in the area of methods and devices to obtain autologous grafts prepared from living vascular tissue.
Vascular grafts are commonly used by surgeons to bypass obstructions to blood flow caused by the presence of atherosclerotic plaques. Vascular grafts also are used to treat other vascular problems. Grafts for bypass are often, but not exclusively, used in the coronary arteries, the arteries that supply blood to the heart. The materials used to construct a vascular graft usually are either synthetic or of biological origin, but combinations of synthetic and biological materials are also under development. The most successful biological vascular grafts are autologous saphenous vein or mammary artery. Some common synthetic grafts are made of polytetrafluoroethylene (PTFE) (GORTEX.TM.) or polyester (DACRON.TM.). Autologous grafts have generally been used more successfully than synthetic grafts. Autologous grafts remain patent (functional) much longer than synthetic grafts, but saphenous veins are seldom functional more than five years. The short lifetime of synthetic grafts is especially evident with small diameter grafts, as most small diameter synthetic grafts occlude within one to two years.
Mammary artery is the autologous graft of choice, because it typically has a longer life than venous grafts (95% patent at 5 years versus 85% patent at 2 years). Mammary arterial tissue, however, is difficult to harvest and typically is not available in lengths sufficient for effective bypass. Moreover, obtaining sufficient venous tissue for repairing an occluded artery is problematic.
In some cases, autologous or homologous saphenous vein preserved by freezing or other processes is used.
With people living longer, multiple surgeries are more common. At the same time, open heart surgery is becoming more routine, aided by the development of new, minimally invasive procedures which have dramatically simplified the surgery and reduced the recovery time. Development of a longer lasting small-diameter vascular graft is the subject of much academic and industrial research. One current approach is to combine cell culture and biomaterials technologies to make a living, "tissue engineered" graft. This effort, however, is hindered by the requirements of a successful graft: it should be self-repairing, non-immunogenic, non-toxic, and non-thrombogenic. The graft also should have a compliance comparable to the artery being repaired, be easily sutured by a surgeon, and not require any special techniques or handling procedures. Grafts having these characteristics are difficult to achieve. Despite the substantial effort to date and the potential for significant financial reward, academic and industrial investigators have failed to produce graft materials which have demonstrated efficacy in human testing.
Efforts to avoid or minimize the need for vascular grafts for repair of otherwise healthy vascular tissue have been described. For example, Ruiz-Razura et al., J. Reconstructive Microsurgery, 10(6):367-373 (1994) and Stark et al., Plastic and Reconstructive Surgery, 80(4):570-578 (1987) disclose the use of a round microvascular tissue expander for acute arterial elongation to examine the effects on the tissue of such acute hyperextension. The expander is a silicone balloon that is placed under the vessel to be elongated. The balloon is filled with saline over a very short period of time, causing acute stretching and elongation of the vessel. The method is purported to be effective for closure of arterial defects up to 30 mm without the need for a vein graft. These techniques are appropriate for trauma, but are not used for restoring blood flow in vessels that are occluded, for example by disease, which are treated by surgically bypassing the obstruction with a graft. The disclosed methods and devices fail to provide an autologous graft or versatile substitute. Moreover, the acute stretching may damage the vessel.
Accordingly, it is an object of the invention to provide a method, and devices therefor, for creating an autologous blood vessel graft.